Production of antimatter in the galaxy

The astronomical dark matter could be made of weakly interacting massive species whose mutual annihilations should produce antimatter particles and distortions in the corresponding energy spectra. The propagation of cosmic rays inside the Milky Way plays a crucial role and is briefly presented. The uncertainties in its description lead to considerable variations in the predicted primary fluxes. This point is illustrated with antiprotons. Finally, the various forthcoming projects are rapidly reviewed with their potential reach. 1. Cosmic ray propagation throughout the Milky Way Supersymmetric neutralinos or Kaluza–Klein particles could explain the dark matter that is indirectly observed around galaxies, inside their clusters and on cosmological scales. These species are hunted for by several experimental collaborations. As they annihilate inside the Milky Way halo, they produce high–energy cosmic rays and in particular antimatter particles such as antiprotons, antideuterons and positrons. These are rare elements which are already manufactured inside the galactic disk through the spallations of primary cosmic rays on the interstellar gas. That conventional process provides the natural background inside which the DM induced antimatter signature may be burried and whose spectral distortions could reveal an exotic signal. It is therefore crucial to derive as precisely as possible the energy spectra of the various antimatter species irrespective of the production mechanisms and to evaluate how well they are known. To reach that goal, a precise understanding of cosmic ray propagation is mandatory. We briefly sketch here how that propagation is understood and how well it is modeled. Interstellar nuclei are accelerated by the passage of supernovae induced shock waves. The sources for primary cosmic ray nuclei are therefore located inside the disk of the Milky Way. Primaries propagate then inside the galactic magnetic fields and undergo collisions on its irregularities – the Alfvén waves. This motion is described in terms of a diffusion process whose coefficient K(E) = K0 βR δ increases with the rigidity R of the cosmic ray particle as a power law. Because the scattering centers move with a velocity Va ∼ 20 to 100 km s −1, a second order Fermi mechanism yields some diffusive reacceleration whose coefficient KEE may be expressed as